…ngtcp2, quiche and msh3 into connection filters.

            - eyeballing cfilter that uses sub-filters for performing parallel connects
            - socket cfilter for all transport types, including QUIC
            - QUIC implementations in cfilter, can now participate in eyeballing
            - connection setup is more dynamic in order to adapt to what filter did really connect.
              Relevant to see if a SSL filter needs to be added or if SSL has already been provided
            - HTTP/3 test cases similar to HTTP/2
            - multiuse of parallel transfers for HTTP/3, tested for ngtcp2 and quiche

            - Fix for data attach/detach in VTLS filters that could lead to crashes during
              parallel transfers.
            - Eliminating setup() methods in cfilters, no longer needed.
            - Improving Curl_conn_is_alive() to replace Curl_connalive() and integrated ssl alive checks into cfilter.
            -  Adding CF_CNTRL_CONN_INFO_UPDATE to tell filters to update connection into and persist it at the easy handle.

            - Several more cfilter related cleanups and moves:
              - stream_weigth and dependency info is now wrapped in struct Curl_data_priority
              - Curl_data_priority members depend is available in HTTP2|HTTP3
              - Curl_data_priority members depend on NGHTTP2 support
              - handling init/reset/cleanup of priority part of url.c
              - data->state.priority same struct, but shallow copy for compares only

            - PROTOPT_STREAM has been removed
              - Curl_conn_is_mulitplex() now available to check on capability

            - Adding query method to connection filters.
              - ngtcp2+quiche: implementing query for max concurrent transfers.
            - struct http is now empty in easy handles, could be removed

            - Adding is_alive and keep_alive cfilter methods. Adding DATA_SETUP event.
                - setting keepalive timestamp on connect
                - DATA_SETUP is called after the connection has been completely setup
                  (but may not connected yet) to allow filters to initialize data members
                  they use.

            - there is no socket to be had with msh3, it is unclear how select shall work
            - manual test via "curl --http3 https://curl.se" fail with "empty reply from server".

            - Various socket/conn related cleanups:
              - Curl_socket is now Curl_socket_open and in cf-socket.c
              - Curl_closesocket is now Curl_socket_close and in cf-socket.c
              - Curl_ssl_use has been replaced with Cur_conn_is_ssl
              - Curl_conn_tcp_accepted_set has been split into
                Curl_conn_tcp_listen_set and Curl_conn_tcp_accepted_set
                with a clearer purpose